1. Field of the Invention
The present invention relates to a method of using a video camera and, more particularly, to a method of using a video camera to detect motion.
2. Description of the Related Art
Video surveillance camera systems are found in many locations and may include either fixed cameras that have a fixed field-of-view (FOV) and/or adjustable cameras that can pan, tilt and/or zoom to adjust the FOV of the camera. The video output of such cameras is typically communicated to a central location where it is displayed on one of several display screens and where security personnel may monitor the display screens for suspicious activity.
Movable cameras which may pan, tilt and/or zoom may also be used to track objects. The use of a PTZ (pan, tilt, zoom) camera system will typically reduce the number of cameras required for a given surveillance site and also thereby reduce the number and cost of the video feeds and system integration hardware such as multiplexers and switchers associated therewith. Control signals for directing the pan, tilt, zoom movements typically originate from a human operator via a joystick or from an automated video tracking system. An automated video tracking (i.e., “autotracking”) system may identify a moving object in the FOV and then track the object by moving the camera such that the moving object is maintained in the central portion of the camera's FOV.
An autotracking system may identify a moving object in the FOV by comparing several sequentially obtained images in the FOV. A change in the content of an individual pixel, or of a localized group of pixels, between sequentially obtained images may indicate the presence of a moving object that needs to be tracked. It is known for an autotracking system to create a “motion mask”, which is a pixel-by-pixel quantification of the amount, or probability, of content change in the pixels between sequentially obtained images. By identifying groupings of pixels that have had changes of content between sequentially obtained images, the system can identify a moving object within the FOV.
There have been identified several problems in relation to the use of autotracking systems. For example, the autotracking system may issue an alarm when it detects a suspicious moving object that could possibly be an intruder. A problem, however, is that the system may issue false alarms when it detects “localized movement”, i.e., background movement, that the system interprets as a suspicious target. An example of a source of such localized movement is a flag waving in the breeze. A related problem is that the presence of localized movement in the field of view may cause inefficiency in tracking actual suspicious targets. Lastly, the presence of localized movement in the field of view may confuse the system and cause the system to lose track of an actual suspicious target.
Conversely, it is possible that it is localized movement that is from an actual suspicious target, and more generalized movement is of less concern. For example, a surveillance camera monitoring a parking garage may frequently sense generalized movement in the form of people walking in and out of the parking garage. However, more localized movement in the form of a would-be criminal lurking next to a doorway would be more suspicious.
Existing pan-tilt surveillance cameras employed to autonomously track motion require the use of various image processing algorithms. The current state of the art is that such systems that autonomously track motion will continue tracking until motion ceases. FIG. 1 illustrates the operation of a current state of the art pan-tilt camera employing autonomous motion tracking. Any general tracking by the camera, as indicated at 10, causes the operator to be notified. The operator may receive a tracking notification if such is enabled in the system. The operator may be able to act upon such tracking if he is presently monitoring the system. During times of unmonitored system operation, tracking continues until motion stops regardless of whether the system is tracking a person (as intended) or tree branches swaying in the wind (unintended operation). During unattended night operations for example, tracking of tree branches near an employee entrance could cause the system to be unavailable for intended usage (i.e., monitoring the entrance) during the entire night.
Although various prior art systems have addressed the need to provide motion masks in a surveillance camera system, none have addressed the need for human involvement and judgment to discern whether a particular source of localized movement is something suspicious that is to be monitored. Nor have any prior art systems notified a user about the presence of localized movement so that the user is able to become involved and make a judgment about the nature of the localized movement.
What is neither disclosed nor suggested by the prior art is a surveillance camera system that can detect and discern between localized and generalized movement; inform a user of the localized movement and where in the field of view the localized movement has been detected; and allow the user to enable and disable the localized movement identification and notification function for particular segments of the field of view.